In electron accelerators used for x-ray radiotherapy, a high-energy electron beam is directed on to an electron-to-x-ray conversion target, typically made of a high-density metal or a combination of layers of various metals. Such targets are generally designed for maximal efficiency of x-ray production while not permitting full or over-penetration by the incident electron beam. The targets are typically water-cooled to withstand the thermal stresses induced in the targets by absorption of the power in the electron beam.
However, if the design of or the production process used in manufacturing the target is faulty, then damage of the materials exposed to the electron beam can occur. Such damage is normally progressive and can result in penetration of the target by the incident electron beam, forming a mix of electrons and x-rays in the radiation beam beyond the target. The consequences of this type of target damage, in addition to changing the intended x-ray output, may extend to errors in the accuracy of the radiation therapy dosimetry measurement system and in other monitors of x-ray beam performance.